The invention relates to a conveying configuration for transporting wafers in clean rooms. The conveying configuration is a transporting store for the wafers and connects a plurality of processing centers for processing the wafers.
Such clean rooms form a constituent part of production facilities for semiconductor products. In particular, the wafers are processed in such production facilities, with the result that the wafers can be used for producing electronic components and the like.
During the processing of such wafers, the purity demands are high, which renders production under clean-room conditions necessary. The process for producing the wafers contains a multiplicity of different processing operations, for example various layer-growing processes, lithography and etching and diffusion processes.
High-outlay processing centers are necessary for each of these processes. During the production process, the wafers have to be fed to the individual processing centers.
In the case of known production installations, the wafers are transported between the individual processing centers by conveying systems defined, for example, as roller conveyors. The wafers are usually transported on the rollers of the roller conveyors in cassettes. A plurality of stockers are disposed on the roller conveyors, in each case a certain number of the stockers are disposed as closely as possible to a processing center. The stockers are stationary storage systems in which the wafer cassettes can be deposited and stored preferably under clean-room conditions. For this purpose, the cassettes with the wafers supplied by the conveying system are removed from the rollers of the conveying system and stored in the respective stocker. This process takes place automatically via handling systems, robots or the like. The capacity of the stockers is such that the respective processing center ensures a sufficient supply of wafers at all times.
In accordance with the requirements of a processing center, a number of cassettes with wafers are retrieved from the stocker, and fed to the processing center, at certain time intervals. In this case, the cassettes may be transported to the processing centers via vehicles that are driven by the operating staff. Alternatively, the transportation may take place via driverless, rail-borne or non-rail-borne vehicles. Transportation back into the stocker or directly back to the conveying system can take place in the same way.
The disadvantage here is that storing cassettes with wafers in the stockers is very costly. On the one hand, this results from the fact that the production costs of such stockers are very high. On the other hand, the stockers have a considerable overall size and, in addition, are required in large numbers. Therefore, a considerable surface area is required, and the clean rooms have to be of correspondingly large dimensions. Finally, the operations of the storage cassettes with the wafers in the stockers and retrieving them from the stockers involve a considerable amount of time since the cassettes have to be moved vertically for positioning purposes and, finally, have to be positioned at defined locations in the stocker. This processing outlay is not just considerably costly, but, such a discontinuous wafer-transporting system results in the overall production capacity being adversely effected.
A conveying system of the type mentioned in the introduction is known from U.S. Pat. No. 5,443,346. The conveying system serves for transporting wafers in a clean room. The conveying system contains an inter-bay conveying system via which the wafers are transported in the cassettes. Branching off from the inter-bay conveying system are intra-bay conveying systems via which the wafers are fed to individual processing stations and, following the processing, are transported away from the processing stations again. An intra-bay conveying system has a conveying rail on which a conveying unit is moved. The conveying unit contains, in particular, a positioning robot. The wafers are introduced into the individual processing stations by the positioning robot. The conveying unit carries along a small selection of wafers that are introduced into the respective processing stations. Since the quantity of wafers delivered in the cassettes via the inter-bay conveying system is larger than the number of wafers transported away via the intra-bay conveying system, there is provided, at the transition between the inter-bay conveying system and an intra-bay conveying system, an interface device in which the wafers are stored.
Published, Non-Prosecuted German Patent Application DE 40 17 006 A1 discloses a wafer-conveying system in which different clean rooms are connected to one another by a closed system of conveying channels. In this case, the conveying system may also be configured, in particular, as a transporting store. In the conveying channels, cassettes with wafers are transported onto transporting belts.
The wafers are transported in the conveying channels under clean-room conditions. For this purpose, filtered air flows through the individual conveying channels.
Provided at crossover points between the individual conveying channels are load locks for loading and unloading the cassettes with the wafers.
The loading and unloading operations at the load locks can be carried out manually by the operating staff. Alternatively, a handling unit may be provided for this purpose.
When a load lock is loaded with a cassette, the destination for the cassette is input via a keyboard.
In principle, an automated flow of the wafers may be realized using such a conveying system.
The disadvantage here, however, is that the cassettes have to be loaded into the conveying system individually one after the other, and also have to be removed therefrom individually, via the load locks. If a plurality of cassettes are supplied at one destination, it is therefore necessary to maintain the order in which the cassettes are to be processed further following removal. This limits the flexibility of the conveying system to a considerable extent.
It is also disadvantageous that the individual removal of the cassettes from the load locks is very time-consuming.
However, on account of the high productivity of the processing centers in semiconductor-production installations, it is necessary for a multiplicity of cassettes of wafers to be available at the processing center simultaneously at certain times.
Accordingly, such a conveying system can be only be used in conjunction with a stocker which is assigned to the respective processing center. The cassettes that have been removed individually from the load locks are then stored in the relevant stocker. Depending on requirements, a predetermined number of cassettes are then simultaneously removed and fed to the processing center.
Published, Non-Prosecuted German Patent Application DE 197 29 525 A1 relates to an apparatus for transporting disc-like substrates, for example digital video discs, from starting stations, via a plurality of process stations, to end stations, the process stations carrying out the processing operations, e.g. coating, monitoring, sorting and collection of the substrates. Gripper arms with grippers or suction devices allow the substrates to be transported further from station to station. There are provided a motor/gear unit with a pivoting device and two lifting devices which can be activated separately from one another and interact with gripper arms. The gear mechanism, which forms a conveying station, is disposed at the same distance away from a plurality of stations, for example the supply station, the coating stations, the return station and the checking station. The two lifting devices of the motor/gear unit simultaneously execute, by way of their gripper arms, identical and/or different lifting movements (vertical movements) and pivoting movements that take place at the same time as the latter or following the latter.
Published, Japanese Patent Application JP 08268512 A discloses a storage device for substrates. The storage device has a rack, it being possible for the substrates to be stored on the rack, and retrieved therefrom, by a loading and unloading unit. The substrates are stored intermediately on a loading bed for sorting purposes.
Published, Japanese Patent Application JP 09235010 A describes the construction of a roller conveyor.
Published, Japanese Patent Application JP 10035883 A discloses a transfer unit via which semiconductor products can be positioned reliably and precisely. In this case, a displaceable receiving device feeds the substrates to predetermined containers. The movement is controlled by a camera system.
European Patent Application EP 0 908 931 A2 discloses as prior art, not published before the priority date of the instant application, a conveying apparatus by which semiconductor products can be fed to different processing stations under clean-room conditions. The conveying apparatus contains a cassette in which the semiconductor products are transported under clean-room conditions. The cassette is transported on rails that likewise form a constituent part of the conveying apparatus. The cassette is introduced, via introduction openings, into the respective processing stations in which the semiconductor products are processed.
It is accordingly an object of the invention to provide a conveying system that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which it is ensured that the wafers can flow, as far as possible, continuously.
With the foregoing and other objects in view there is provided, in accordance with the invention, in combination with a clean room having a plurality of processing centers for processing wafers, a conveying configuration for transporting the wafers to and in the clean room, the conveying configuration including:
a main conveying system functioning as a transporting store for the wafers; and
a plurality of secondary conveying systems branching off from the main conveying system, each of the plurality of secondary conveying systems leading, at a minimum, to one processing center and forms a supply buffer from which a predetermined number of the wafers can be removed and fed to the processing center.
The conveying system according to the invention, which is configured as a transporting store and is intended for transporting wafers, connects a plurality of processing centers for processing the wafers. Secondary conveying systems branch off from the conveying system. In each case one secondary conveying system leads to a certain processing center and forms a supply buffer. From the secondary conveying system, a predetermined number of wafers can optionally be removed, and fed to the processing center, by use of a handling unit.
The conveying system according to the invention ensures that the wafers flow continuously. A considerable advantage resides here in the fact that no stockers are required for storing the wafers.
By virtue of suitable dimensioning of the conveying system, the wafers are stored on the conveying system itself. From the conveying system, the number of wafers that is required in each case is guided directly to the processing center via the respective secondary conveying system. It is particularly advantageous here for the secondary conveying system itself to act as the supply buffer. This is achieved by suitable dimensioning of the secondary conveying system.
In this case, the individual wafers on the secondary conveying system are simultaneously accessible to the handling unit. For example, the secondary conveying system has a predetermined number of roller conveyors, on the top sides of which the wafers in the cassettes rest one behind the other. The handling unit then picks up, at defined receiving locations in each case, the required cassette and feeds it to the processing center. The freely selectable access of the handling unit on the secondary conveying system to the cassettes holding the wafers provides a flexible system for reacting to different wafer demands, in particular, to wafer load peaks.
A further advantage of the conveying system according to the invention is that it is of modular construction and can easily be adapted to changing production outputs.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a conveying system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.